I've been following this discussion for some time now, and eventually decided to take a gamble and pick up 200 shares of ATCO. I figured I could afford to lose $1,000 if the whole thing went belly-up, which it might. So far, I've taken a real bath on this, but that's to be expected until something happens. (Carl, feel free to say "I told you so".)
The message from Connie Sabon of ATC responding to the missive from Carl's technical guru was very interesting, and seems to hold water as far as it goes, but still leaves me with a number of questions about the technology. I'm hoping someone can forward these questions to her and post her answer here.
Here goes (please pardon my ignorance of acoustics)...
At first, I thought that the way HSS worked was that what traveled through the air were ultrasonic signals, and that our ears heard the interference ("beats") between them as audible sound, a kind of "aural illusion". From this last description, it sounds more like what happens instead is that the interfering ultrasonic signals cause ACTUAL SOUND to be generated in the air-- something about the intertia of the air molecules and the interference of the ultrasonic waves causes waves of the difference frequency to actually be present and propagated through the air. The ear doesn't "synthesize" the sound from the interference between the ultrasonic signals-- the interference between the ultrasonic signals produces real sound, which the ear hears like it would hear any other sound.
So the fact that the inertia of the air molecules absorbs energy in the ultrasonic signal, causing it to die off quickly, doesn't matter. The ultrasonic signal only has to be strong enough to excite the real sound in the vicinity of the speaker, and that sound then propagates the way it normally would.
As I understand it, rather than having two separate drivers, one with the carrier frequency and one with the modulated signal, the HSS system mixes them electronically before sending them to the drivers. So it doesn't rely on the interference happening in the air-- it's already present in the signal as it comes off the driver.
This doesn't seem to jibe with some of the claims being made for HSS. Sound gets more directional as it increases in frequency. If the ultrasonic signals made "sound" in our heads, then some of the claims for how the apparent sounrce of the sound can be manipulated by where you point the driver would make sense. But if instead real sound waves are produced in the air around the speaker by the ultrasonic signals, and THAT'S what we hear, then it seems like the sound would have to be appearing to come from some fixed position in front of the driver and would spread out from that point in a less directional way.
In other words, the description suggests you could put two HSS drivers at the back of the room right next to each other and point them at spots on the front wall and the sound would appear to come from those spots on the front wall (unless you were blocking the beam). But if an HSS driver produces regular sound in the air around it, it wouldn't be that directional and you'd hear the sound coming from the HSS driver itself.
So where does the sound really come from and how can you manipulate its apparent source?
The second question is similar to the first. If the sound is produced in our ears from the ultrasonic signal, we could get deep and accurate bass, but without the tactile effect we normally expect from loud, deep bass. If the HSS driver produces real sound, however, you'd get the tactile effect, but bass would be no more impervious to room acoustics than it is when you produce it any other way. The bass signal would still set up standing waves in a rectangular room, leading to "hot" and "cold" spots at certain frequencies, rather than uniform frequency response throughout the room, as HSS's proponents seem to be claiming. So again, if the HSS driver produces real sound, why would bass from it be any more directional and less impervious to room acoustics than bass from a conventional subwoofer?
Even if the things I'm seeing as problems are true, HSS would still be a big leap forward in speaker design (if it works at all). What you'd get would essentially be an ideal point source, with all the sound appearing to come from a single spot with flat frequency response, low distorion, perfect phase coherence, no cabinet resonances or diffraction effects, and much greater efficiency (not to mention simpler ease of placement). But it wouldn't do some of the things that are being claimed for it.
I'm sure this posting has amply demonstrated my ignorance of acoustics, so I'm hoping someone out there with real expertise (preferably someone at ATC) can clear up my misconceptions for me.
Thanks a lot...
--Rich |
